Lenovo Ideacentre A600 Problem

When i turn on the computer, it switch off suddenly. i tried to turn on again and again, but it will switch off agian and again. Then, sometimes, it will occur the error about 'boot sequence error'. I can press F1 / any key to Lenovo BIOS Setup Utility. I tried to press F9 to load the default in BIOS, but nothing. Hope helpers can step by step to teach me.

Thanks for the help! T.T

Information of my computer:

IdeaCentre A600
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CPU / PentiumR Dual-Core CPU T4400 2.2GHz

CPU Speed / 2200MHz

CPU Bus Speed / 800MHz

CPU Core Count / 2

Installed Memory / 4096MB

Memory Bus Speed / 1066MHz

ATI MXM M96M Graphics

Onboard Audio / Enable

Onboard Ethernet / Enable

CPU Fan / 191

System Fan / 1437

MXM Temperature / 53 C

SATA DRIVE 0 / Hitachi HDT721064SLA360 (PM)

SATA DRIVE 1 / Optiarc DVD RW AD-7640S (PS)
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